1. Field of the Invention
The present invention relates to a control device for a hybrid vehicle.
2. Description of the Related Art
Conventionally, in a hybrid vehicle which comprises an engine and a motor that is capable of generating electrical power (hereinafter referred to as a xe2x80x9cmotor-generatorxe2x80x9d) as power sources, and in which the power of at least one of the engine and the motor-generator is transmitted to an output shaft for driving the hybrid vehicle, when a state of charge of a battery (hereinafter simply referred to as xe2x80x9cSOCxe2x80x9d) as an energy storage means is in a normal state, a control operation is executed in such a manner that the drive mode of the hybrid vehicle is switched between an engine drive mode and a motor drive mode depending on a vehicle speed, a running resistance, and an opening degree of a throttle so as to obtain high efficiency.
Moreover, in such a hybrid vehicle, the power of driving wheels during deceleration is transmitted to the motor-generator so as to convert deceleration energy into regenerated energy, and the regenerated energy, as electrical energy, is stored in a battery device (see, for example, Japanese Unexamined Patent Application, First Publication No. 2001-169406). Conventionally, in such a case, a control operation is executed so that the amount of regenerated energy is restrained in order to protect the battery when the SOC of the battery is above a predetermined value.
However, when the amount of regenerated energy is restrained as mentioned above, degree of deceleration of the vehicle is decreased as shown in FIG. 8, and a problem is encountered in that the driver experiences unnatural sensations.
Moreover, when the amount of regeneration is restrained, the amount of regenerated energy is reduced, and energy at braking operations is dissipated as heat. As a result, a problem is encountered in that fuel economy is degraded.
Based on the above circumstances, an object of the present invention is to provide a control device for a hybrid vehicle, which enables restraining decrease in degree of deceleration of the vehicle during a regenerative operation.
Another object of the present invention is to provide a control device for a hybrid vehicle, which enables improvement in fuel economy by broadening a motor drive zone, and by increasing the amount of regenerated energy.
In order to achieve the above objects, the present invention provides a control device for a hybrid vehicle which comprises an engine and a motor that is capable of generating electrical power as power sources, and in which the power of at least one of the engine and the motor is transmitted to an output shaft for driving the hybrid vehicle, the control device comprising: an energy storage section which is capable of supplying energy to the motor; a state of charge measuring section for measuring the state of charge of the energy storage section; and a drive control section that preliminarily stores information of a motor drive permissible vehicle speed below which a motor drive mode, in which the engine outputs no power and the motor is operated solely for driving the hybrid vehicle, is employed, wherein the drive control section is adapted to control so to increase the motor drive permissible vehicle speed when the state of charge of the energy storage section measured by the state of charge measuring section is equal to or greater than a predetermined value.
According to the control device for a hybrid vehicle configured as described above, it is possible to broaden a drive zone in which the vehicle is driven solely by the power of the motor (hereinafter this zone is referred to as a xe2x80x9cmotor drive zonexe2x80x9d), and as a result, regenerated energy can be recovered without decreasing the amount of regeneration.
In the above control device, the engine may be adapted to perform a cylinder deactivation operation, in which the operations of associated intake and exhaust valves are suspended, on at least some of cylinders thereof in the motor drive mode in which the engine outputs no power.
According to the control device configured as described above, it is possible to reduce pumping loss in the engine, and thus it is possible to reduce engine friction when the vehicle is driven by the motor.
Note that the cylinder deactivation operation may be applied to all of the cylinders, or alternatively, may be applied to some of the cylinders.
In the above control device, the motor drive permissible vehicle speed may be set so as to be gradually increased as the state of charge of the energy storage section increases.
According to the control device configured as described above, the state of charge of the energy storage section may be prevented from being excessively reduced due to drive by the motor at a high vehicle speed when the state of charge of the energy storage section is at a low level.
In the above control device, the drive control section may be further adapted to control so as to lower the motor drive permissible vehicle speed to the level before being increased when the state of charge of the energy storage section measured by the state of charge measuring section becomes less than the state of charge corresponding to the motor drive permissible vehicle speed after being increased.
According to the control device configured as described above, it is possible to set the motor drive permissible vehicle speed to the level before being increased when the state of charge is reduced.
In the above control device, the state of charge corresponding to the motor drive permissible vehicle speed after being increased may be provided with hysteresis that is set depending on the motor drive permissible vehicle speed.
According to the control device configured as described above, it is possible to reduce the state of charge of the energy storage section by at least an amount corresponding to hysteresis when the motor drive mode is selected based on the increased motor drive permissible vehicle speed. In addition, a hunting phenomenon, in which the drive mode is frequently switched into the motor drive mode and switched out of the motor drive mode, may be avoided.
In the above control device, a motor drive permissible period after the motor drive permissible vehicle speed is increased may be preliminarily set depending on the vehicle speed and the state of charge of the energy storage section. Here, the xe2x80x9cmotor drive permissible periodxe2x80x9d means time during which single and continuous drive by the motor is permitted.
According to the control device configured as described above, because energy consumed in the motor drive mode is determined depending on the vehicle speed and the motor drive permissible period, the state of charge of the energy storage section after executing drive by the motor may be set in advance.
The present invention further provides a control device for a hybrid vehicle which comprises an engine and a motor that is capable of generating electrical power as power sources, and in which the power of at least one of the engine and the motor is transmitted to an output shaft for driving the hybrid vehicle, the control device comprising: an energy storage section which is capable of supplying energy to the motor; a state of charge measuring section for measuring the state of charge of the energy storage section; a cylinder deactivation executing section which executes a cylinder deactivation operation on at least some of cylinders of the engine by suspending the operations of associated intake and exhaust valves; and a drive control section which is adapted to control the cylinder deactivation executing section, when the motor performs a regenerative operation during deceleration of the hybrid vehicle, so as to execute a cylinder deactivation operation when the state of charge of the energy storage section measured by the state of charge measuring section is equal to or less than a predetermined value, and so as to prohibit a cylinder deactivation operation when the state of charge of the energy storage section measured by the state of charge measuring section is greater than the predetermined value.
According to the control device for a hybrid vehicle configured as described above, when the state of charge of the energy storage section is at a low level during regenerative deceleration, it is possible to reduce pumping loss in the engine by executing the cylinder deactivation operation, and thus it is possible to increase regenerated energy by an amount corresponding to the reduced pumping loss. On the other hand, when the state of charge of the energy storage section is at a high level during regenerative deceleration, it is possible to increase pumping loss in the engine by prohibiting the cylinder deactivation operation, and thus it is possible to increase degree of deceleration of the vehicle.
Note that the cylinder deactivation operation may be applied to all of the cylinders, or alternatively, may be applied to some of the cylinders.
In the above control device, the drive control section may be further adapted to set the amount of regeneration, when the cylinder deactivation executing section is prohibited to execute a cylinder deactivation operation, to be less than that in a state in which the state of charge is equal to or less than the predetermined value.
According to the control device configured as described above, increase in the engine friction due to prohibition of cylinder deactivation operation may be compensated for by decreasing the amount of regeneration. Note that the amount of regeneration may be controlled by a regenerative output control section.
In the above control device, the drive control section may be further adapted to gradually decrease the amount of regeneration as the state of charge of the energy storage section increases.
According to the control device configured as described above, the increasing rate of the state of charge of the energy storage section may be slowed down.